diff --git a/src/Pgvector/SparseVector.cs b/src/Pgvector/SparseVector.cs
index 448ccf9..5843666 100644
--- a/src/Pgvector/SparseVector.cs
+++ b/src/Pgvector/SparseVector.cs
@@ -55,6 +55,11 @@ public SparseVector(ReadOnlyMemory<float> v)
 
     public SparseVector(IDictionary<int, float> dictionary, int dimensions)
     {
+        if (dimensions < 0)
+        {
+            throw new ArgumentOutOfRangeException(nameof(dimensions));
+        }
+
         var count = 0;
         var capacity = dictionary.Count;
         var indices = new int[capacity];
@@ -64,6 +69,12 @@ public SparseVector(IDictionary<int, float> dictionary, int dimensions)
         {
             if (e.Value != 0)
             {
+                if (e.Key < 0 || e.Key >= dimensions)
+                {
+                    throw new ArgumentOutOfRangeException(
+                        nameof(dictionary), e.Key, "Dictionary keys must be within the vector dimensions.");
+                }
+
                 indices[count] = e.Key;
                 values[count] = e.Value;
                 count++;
diff --git a/tests/Pgvector.CSharp.Tests/SparseVectorTests.cs b/tests/Pgvector.CSharp.Tests/SparseVectorTests.cs
index 2b66115..a288438 100644
--- a/tests/Pgvector.CSharp.Tests/SparseVectorTests.cs
+++ b/tests/Pgvector.CSharp.Tests/SparseVectorTests.cs
@@ -40,6 +40,21 @@ public void DictionaryConstructor()
         Assert.Equal(new float[] { 1, 2, 3 }, v.Values.ToArray());
     }
 
+    [Theory]
+    [InlineData(-1)]
+    [InlineData(6)]
+    public void DictionaryConstructorRejectsIndicesOutsideDimensions(int index)
+    {
+        var dictionary = new Dictionary<int, float> { [index] = 1 };
+        Assert.Throws<ArgumentOutOfRangeException>(() => new SparseVector(dictionary, 6));
+    }
+
+    [Fact]
+    public void DictionaryConstructorRejectsNegativeDimensions()
+    {
+        Assert.Throws<ArgumentOutOfRangeException>(() => new SparseVector(new Dictionary<int, float>(), -1));
+    }
+
     [Fact]
     public void Equal()
     {